Pumps utilized for pumping abrasive fluids, specifically slurries, are conventionally provided with an enlarged-bore seal chamber through which a rotatable pump shaft projects, and a mechanical seal assembly is traditionally mounted in this chamber for creating a sealed relationship between the shaft and the surrounding housing. It has long been observed, however, that this arrangement causes undesirably rapid wear particularly of the seal assembly and specifically the gland ring which fixes to the housing when the fluid being handled is abrasive, such as a slurry. The operation of the pump causes some of the pumped fluid to circulate within the enlarged-bore seal chamber in surrounding relationship to the mechanical seal, and this circulation causes the fluid to move both circumferentially and axially in the chamber. The abrasive fluid thus undergoes a flow reversal adjacent the gland which, coupled with rotational centrifugal effects on heavier particles which tend to collect in the outer corner of the chamber, effect erosion and hence wear of the gland ring at an undesirably rapid rate. This thus necessitates repair and maintenance of the seal assembly at a more frequent than desired interval.
In an effort to minimize such erosion-induced wear, some pumps have recently been provided with axially-extending protrusions fixed to or adjacent the outer wall of the enlarged-bore seal chamber, with these protrusions projecting axially inwardly from adjacent the gland of the seal assembly. These protrusions have been observed to at least provide some improvement in the fluid circulation pattern with respect to minimizing at least erosion-induced wear on the pump housing itself, but it has been observed that most of the proposals and structures have so far failed to significantly minimize or eliminate erosion-induced wear of the gland ring.
Typical known proposals or structures involving protrusions or flow modifiers within the enlarged-bore seal chamber are illustrated by FIG. 1, and are explained in greater detail hereinafter.
Attention is also directed to the paper entitled "Enhanced Mechanical Seal Performance Through Proper Selection and Application of Enlarged-Bore Seal Chamber", Proceedings of 10th International Pump Users Symposium, 1993, wherein this erosion problem and the proposed use of protrusions as flow modifiers are described in detail.
It is an object of this invention to provide an improved erosion protector or flow modifier for disposition within an enlarged-bore seal chamber in surrounding relationship to the mechanical seal so as to greatly minimize erosion-induced wear of the gland ring when the pump is handling abrasive fluids such as slurries. The improvement of this invention is believed to provide a significantly greater reduction in erosion-induced wear, such as when handling abrasive fluids, than was possible with prior structures and proposals.
According to the present invention, a mechanical seal is disposed in surrounding relationship to a pump shaft within an enlarged-bore seal chamber defined by the pump housing to create a sealed relationship therebetween. The mechanical seal assembly includes a gland ring which is stationarily fixed to the pump housing for closing off the outer end of the enlarged-bore seal chamber. An annular erosion protector or flow modifier according to the invention is disposed within the enlarged-bore chamber in close and generally overlapping relationship to the inner axial face of the gland ring, with this annular protector having axially projecting protrusions which project axially inwardly along the outer portion of the enlarged-bore chamber. The protector preferably occupies a significant part of the volume of the enlarged-bore chamber to minimize the quantity of pump fluid entering therein, and is effective in significantly eliminating direct erosion-contact of the pump fluid against both the gland ring and the surrounding wall of the seal chamber. The annular protector is preferably stationarily but removably attached to the gland ring so as to permit it to be readily removed and replaced when worn, whereby shutdown and repair of the seal can be accomplished quickly and economically.
In the improved arrangement of the present invention, as aforesaid, the annular erosion protector preferably includes an annular wall part provided at the axially outer end thereof and projecting radially inwardly so as to effectively cover the gland ring, with this latter annular wall part having an inner annular edge which in a preferred embodiment is substantially maintained in sealing engagement with the non-rotatable face ring of the seal assembly.
In the improved arrangement, as aforesaid, the protector ring may in one embodiment be constructed integrally of one-piece or alternatively the protector may have separate annular parts, one defining the projections thereon and the other projecting radially inwardly for covering the gland face, with these two annular parts being constructed of different materials if desired.
In the improved arrangement of the present invention, as aforesaid, the annular protector can be formed of a suitable material, either a hard or a soft material, depending upon the nature of the abrasive fluid being handled.